Ultrahigh Temperature Flash Sintering of Binder-Less Tungsten Carbide within 6 s

Abstract

We report on an ultrarapid (6 s) consolidation of binder-less WC using a novel Ultrahigh temperature Flash Sintering (UFS) approach. The UFS technique bridges the gap between electric resistance sintering (≪1 s) and flash spark plasma sintering (20–60 s). Compared to the well-established spark plasma sintering, the proposed approach results in improved energy efficiency with massive energy and time savings while maintaining a comparable relative density (94.6%) and Vickers hardness of 2124 HV. The novelty of this work relies on (i) multiple steps current discharge profile to suit the rapid change of electrical conductivity experienced by the sintering powder, (ii) upgraded low thermal inertia CFC dies and (iii) ultra-high consolidation temperature approaching 2750 °C. Compared to SPS process, the UFS process is highly energy efficient (≈200 times faster and it consumes ≈95% less energy) and it holds the promise of energy efficient and ultrafast consolidation of several conductive refractory compounds.

On the confluence of ultrafast high‐temperature sintering and flash sintering phenomena

“…Recently translucent alumina has been produced 9 . Even electronic conductors such as tungsten carbide 10 and silicon carbide 11 have been sintered in this way. Corning, Inc. has developed the process for continuous production of (flexible) thin strips of aluminum oxide 12…”

Effects of processing conditions on flash sintering of commercial ZrN

“…It must be mentioned that such a hypothesis is consistent with some very recent studies on FS for tungsten carbide as well as metallic tungsten that suggest the critical role of less conductive surface layer (amorphous carbon or oxide) over conductive powder surface in enabling the flash event for these materials. 19,21,42,43 Further verification using both extensive materials characterization and computation modeling based on the finite element method will be carried out in the future to verify such a hypothesis and, possibly distinguish the contributions from particle packing/densification and fracture or breakdown of low conductivity (oxide or other) shells.…”

“…29,30 Other factors include (partial) electrochemical reductions 31,32 and dielectric breakdown. 33,34 Although a few studies have been carried out on FS of highly conductive HTCs, such as borides, carbides, and nitrides, 14,[16][17][18][19][20][21] there have not been many efforts to systematically characterize the detailed flash behavior for these materials and delve into possible mechanisms. As shown in Figure 2, the conductivity-temperature relationship of several highly conductive HTCs including ZrN is like metals, meaning when temperature increases, ZrN bulk conductivity would decrease, 3 which is opposite to that for YSZ and would, in theory, work against the FS phenomenon.…”

Top priority current path between SiC particles during ultra-high temperature flash sintering: Presence of PyC “bridges”

“…SiC is a semiconductor with a large band gap and is affected by the high Schottky barrier at the ceramic grain boundary [29,30]. The electrical properties of SiC as a semiconductor or even an insulator do not meet the requirements of FS [31][32][33][34]. Al 2 O 3 and Y 2 O 3 used as FS aids for SiC can locally approach the theoretical density under the assistance of an electric field of 100 V/cm [28].…”